first arrived in 2004, it was the beginning of the so-called “four-door coupe” movement. Even if the terminology still rubs people the wrong way, the style itself has taken off and even influenced SUVs. But as the genre evolves,

has always kept its CLS true to the original. Now in its third generation, the 2019 CLS retains much of the look of its predecessors, perhaps because to change it too much would ruin it.

Though it might not look like it from the outside, there are a lot of tweaks that move the new CLS into the future, particularly under the hood. As we prepared to get behind the wheel for the first time, Peter Kolb, the man in charge of vehicle testing for the CLS, told us, “We have perfected the original.” We headed to the scenic mountains of the Catalonian countryside to see for ourselves.

The main thrust of the styling changes was to remove distracting visuals for a cleaner overall look. The profile still bears a swoopy silhouette with a long nose and tiny bubble of a greenhouse behind it, but the sheet metal is smoother and rounder, with no major sharp creases to focus in on. CLS designer Uwe Haller described it as Design Philosophy 2.5, which he explained like this: “Leave a line off. If it looks good, leave another line off.” This thinking works for us, as we find the new CLS’s profile to be a near-perfect distillation of the four-door coupe concept.

Up front, we love the way the hood is completely separated from the lighting, surrounded on all sides by body. The “shark nose” comes to an aggressive point in front of the vehicle, and the slim headlights look clean and fast on their own. The grille, with its diamond design, and the functional aero bits up along the bottom and at the sides, add some visual interest. This car has a drag coefficient of 0.29, and it looks every bit that slippery.

In the rear, the flat deck flips up into a tidy little spoiler, which helps provide downforce and stability at higher speeds. The new two-piece taillights are bisected by the opening of the trunk, and they look sporty and angular — an appropriate visual finale as the car slinks past you. Depending on the version of the CLS, either one or two exhaust tips on either side are separated by a rear diffuser.

The car’s interior feels like a significant update. Gone is the devotion to stodgy, conservative styling of eras past. The CLS adopts the interior treatment pioneered by the

, which embraced the latest technology. The new CLS’s interior finally feels just as sexy and charismatic as the focused exterior.

Inside, the wave line, highlighted by mood lighting, draws your eye from one door, down the dash and across the other door — and even across the rear doors if you crane your neck. In front of the driver, the CLS is updated with a pair of digital screens under a single, continuous pane of glass, an elegant incorporation compared with the previous monolithic look of the central tablet. One serves as the instrument panel, the other as an infotainment display. The leather stretched across the dash and over the seats of our tester’s Designo interior is smooth and soft. Perhaps the most interesting visual feature inside the CLS, though, is the jet-turbine look of the round, illuminated air vents. Lighting around the knob in the center changes from blue when blowing cool air to red when providing heat.

Apart from the lack of overhead airspace, the interior of the CLS feels particularly roomy. There’s a lot of space between the front occupants, and it’s wide enough for a middle seat in the back — a first for the CLS. That low-slung roofline does mean you taller folks will have to take off your cowboy hat before you get in. At 6 feet tall, moving our seat as low as it would go did allow us to forget about the headroom issues after a bit.

The most intriguing change to the CLS isn’t an aesthetic one. Instead, it’s under the hood, in the form of an inline six-cylinder engine with a 48-volt

In practice, the inline-six in the CLS450 is truly a pleasure to use. For one thing, it sounds interesting. The little bit of noise that makes its way in from under the hood is very mechanical and controlled; it’s really easy to picture the tiny, perfectly timed individual explosions ticking off in their respective cylinders. There’s a comforting smoothness in that configuration in terms of putting power down, first familiar to your author from a

. Mercedes’s new inline-six really is an interesting motor in terms of technology, safety, efficiency, cooling and NVH.

The inclusion of the 48-volt EQ Boost system, with its additional 22 horsepower and 184 pound-feet of torque (yes, you read that correctly), is part of what makes this powertrain so satisfying to use. Normally, mild hybrid systems feel passive, unnoticed by the driver except when the engine shudders to life when a stoplight turns green. Uniquely, Mercedes showcases this system to the driver with a single, linear gauge on the instrument panel, with the meter moving to the left during charging, and right during boosting. This allows the driver to correspond the acceleration they feel to what the system is actually doing. It feels playful, and introduces into this gas-powered

The rest of the driving dynamics are familiar. The nine-speed automatic transmission shifts smoothly, quickly and quietly in the 450. The steering is typically uncommunicative, but we didn’t find any difficulty in aiming the slinky CLS along the narrow mountain roads of Catalonia, though some of the bus drivers near Monestir de Montserrat seemed to have even more confidence than us. Even in the rain, putting our foot to the floor in our AWD test car was met with faultless stability.

In the AMG CLS53, everything is more amplified. Output is boosted to 429 horsepower and 384 pound-feet with the help of a twin-scroll turbocharger electric auxiliary compressor. It also benefits from the same temporary power bump from the EQ Boost starter-alternator. From the driver’s seat, the sound of this turbocharged version is more dominated by the exhaust. The shifts from the AMG-tuned nine-speed transmission are met with blats from the four exhaust tips in the rear. The 0-to-60-mph run comes in a snappy 4.5 seconds, three-tenths of a tick faster than in the 450 4Matic. The steering feels tighter, more responsive and even a bit more communicative about the road surface. We were able, on just a couple occasions, to elicit just a wee bit of squirreliness from the rear end when accelerating out of a tight, wet corner.

Mercedes-Benz has been a leader when it comes to intelligent driver assistance systems, and now cruise control is getting even smarter. The CLS borrows its Distronic technology from the

. It has adaptive cruise control and lane following. The neat trick here, though, is that it will automatically adjust for changing speed limits, and it even anticipates curves in the road and slows down for them. On the windy Spanish highways, we were truly impressed to see the car navigate corners on its own. It did so cautiously, and at lower cornering speeds than we’d have maintained under manual control. No surprises there, as safety and comfort come first.

So, is this the perfect CLS? Let’s go down the list.

Exterior design? Nailed it.

Interior? The space, materials and overall design go in the win column. It’s the appearance of the techy stuff that stands to age less gracefully. We’ll call it mission accomplished for now, though we’ll be interested to take another look at the third-generation CLS close to the end of its life cycle to see whether we still dig those screens and illuminated vents.

Technology? Spot on. The driver assistance tech, in particular, is nice to have in a grand tourer like this.

Powertrain? Nailed it. We loved both iterations of this inline-six and hope to see it in more vehicles soon. The EQ Boost system takes an already solid format and makes it feel advanced. Routing power through a smooth, no-fuss nine-speed automatic with paddle shifter seems like the ideal, well-rounded choice for the CLS.

Driving dynamics? It does a good job of being a CLS. It’s not a car you take to the track and beat to hell. It’s a car for eating up miles quickly, comfortably, not to mention stylishly. As such, yeah, Mercedes nailed it.

The third-generation might be damn close to the being the perfect CLS. There’s only one thing in the near term that could change that: the